The invention relates to a luminaire comprising:
a concave reflector having an optical centre on said axis, a light emission window, and a reflecting surface which surrounds the optical axis, is built up from plane facets, and has a plane of symmetry, which facets
are arranged in rows which each extend to the light emission window between first planes, and in addition
are bounded by second planes which are substantially parallel to one another and transverse to the first planes;
means for accommodating an electric light source inside the reflector in a plane transverse to the plane of symmetry and in the optical centre.
Such a luminaire is known from U.S. Pat. No. 4,929,863.
The known luminaire is rotationally symmetrical and suitable for forming a narrow beam from the light generated by an electric lamp with a comparatively short light source. The luminaire may thus be used for illuminating buildings with a height of 100 m or more, such as towers. The known luminaire may also be used for lighting large areas, such as sports stadiums, in that luminaires are positioned along the circumference. Because of the narrow beam, the luminaires do have to be placed on comparatively high masts of, for example, 50 m or more.
The plane facets in the known luminaire are arranged not only in rows which extend to the light emission window while being bounded by first planes, but also in continuous circumferential bands which are bounded by parallel second planes which are perpendicular to the axis of the reflector.
It is a limitation of the known luminaire that only a small portion of an object positioned at a comparatively small distance from the luminaire can be illuminated owing to the narrowness of the beam, and only with a very high local illuminance, too high for many applications.